This invention relates in general to the field of electronic devices. More specifically this invention relates to an apparatus and method for cleaning a vertical furnace pedestal and cap.
Semiconductor fabrication environments are typically required to maintain high levels of cleanliness. Impurities associated with wafers, processing equipment, and operators may lead to defects in the semiconductor devices manufactured, often rendering them unusable for their intended purpose. These defects often have serious negative effects on product yield and profitability. Semiconductor fabrication typically takes place in so-called clean room environments where operators wear non-linting garments, overshoes, gloves, and masks to limit the introduction of contaminate particles into the fabrication environment. Semiconductor substrate wafers are often processed during fabrication to remove contaminates and impurities.
Vertical furnaces are often used to facilitate high temperature processing of multiple semiconductor substrate wafers. Often, a heated process fluid enters the vertical furnace through an inlet at a bottom portion of the vertical furnace. Process fluid then flows through the vertical furnace before exiting through an exhaust outlet. The vertical furnace typically has an interior cavity sized to allow a wafer carrier assembly, often referred to as a boat assembly, to be loaded inside the cavity and an automated elevator apparatus to insert and remove the boat assembly in and out of the furnace cavity. However, some vertical furnaces may be loaded manually.
The boat assembly supports multiple substrate wafers during processing within a vertical furnace. The boat assembly typically includes a wafer carrier or boat, and a pedestal and a cap that support the boat. The pedestal often includes insulating quartz baffles. Because process fluid typically enters the vertical furnace adjacent to the baffles, impurities and contaminates often collect on the pedestal. Impurities also collect on the pedestal and cap because it may located beneath wafer loading equipment and because particles within the vertical furnace often fall within the interior of the furnace, where the pedestal and cap are located during processing. These impurities can later dislodge and contaminate the substrate wafers being treated within the vertical furnace.
The pedestal and cap can be cleaned manually to remove accumulated contaminate particles. However, this cleaning interrupts fabrication processes, consuming valuable time and resources. Often, manual cleaning is periodic, taking place only after several process runs and after impurities and contaminate particles have built up on the pedestal. Also, manual cleaning within a controlled process environment can disturb the process environment by introducing dislodged impurities and cleaning medium therein.
In accordance with teachings of the present invention, a system and method for cleaning a vertical furnace pedestal and cap are described which substantially eliminate or reduce disadvantages and problems associated with prior systems and methods. The system includes at least one inlet conduit in fluid communication with a pressurized cleaning medium source. The system also includes at least one exhaust conduit in fluid communication with a negative pressure source. A boat assembly may be positioned such that the at least one conduit is operable to direct a cleaning medium at the boat assembly to dislodge contaminate particles associated with the boat assembly. The exhaust outlet then evacuates the cleaning medium and any dislodged contaminate particles. The system may operate automatically within a closed processing environment. Additionally the system may clean the boat after each process cycle. The exhaust conduit acts to remove the cleaning medium and any dislodged particles to maintain a desired level of cleanliness within the process environment.
In one aspect of the present invention the vertical furnace system includes a boat assembly with a pedestal. The boat assembly is operable to be disposed within a vertical furnace. The system also includes at least one inlet conduit that communicates a cleaning medium from a pressurized cleaning medium source and directs the pressurized cleaning medium at the pedestal to dislodge impurities associated with the pedestal. At least one exhaust conduit is in fluid communication with a negative pressure source and is operable to evacuate the cleaning medium and any dislodged impurities.
More specifically, the boat assembly further includes a boat for securing at least one substrate wafer. The pedestal supports the boat and preferably includes an insulating baffle or disks disposed in a substantially horizontal position spaced from one another. A cap may be coupled to the pedestal distal the boat. The cap is preferably operable to form a seal when disposed adjacent to a bottom portion of the vertical furnace.
In another aspect of the present invention, the system includes at least one inlet conduit and at least one exhaust conduit. The at least one inlet conduit is in fluid communication with a pressurized cleaning medium source operable to direct a pressurized cleaning medium at a boat assembly. The at least one exhaust conduit is in fluid communication with a negative pressure source and is positioned to receive the cleaning medium exiting the at least one inlet conduit.
More specifically at least one flow control device may be disposed between the pressurized cleaning medium source and the at least one inlet conduit. The flow controller may selectively allow a pulse or series of pulses of pressurized cleaning medium to exit the pressurized cleaning medium source and communicate to the at least one inlet conduit.
In yet another aspect of the present invention a method for cleaning a boat assembly during semiconductor processing includes placing the boat assembly in a cleaning position. A pressurized cleaning medium is then directed at the boat assembly to dislodge impurities associated with the boat assembly. The pressurized cleaning medium and any dislodged impurities are then evacuated through an exhaust conduit in fluid communication with a negative pressure source. More specifically, the method includes directing a pressurized pulse of cleaning medium at the boat assembly.